Hello!
I was preparing a hollow cube (4x4x4 cm) in Blender. When I uploaded it as STL the Shapeways servers did consider it as hollow giving it a volume of 33 cm3.

However, when I did a UV-mapping with JPG images and uploaded it as VRML97 (zipped with image files) the server returned a value of 64cm3, which is a volume of a solid cube of that size. All other parameters were as before, only UVmaps were added.

I played with various ways of making a hollow object but every time I apply UVmaps tha volume jumps to that of a solid object.

Do you possibly know why this is happening and how can I overcome this obstacle?

Is there a throu hole? or is it just a hollow cube? If it's just a hollow cube, than the VRML is acting properly and the STL is not (or at least not as it has been said to be working) If there is a hole then vice versa. The software should detect any geometry without and escape hole and get rid of it.

I learned a long time ago the wisest thing I can do is be on my own side, be an advocate for myself and others like me. -Maya Angelou
michael@shapeways.com Community Advocate

I don't know how Blender applies UV maps (i don't get on with blender), but I just used your hollow cube model imported into Wing3D, applied a UV map and uploaded as a VRML, volume is 33.15cc with 4cm sides - looks like the issue might be with Blender.